The present invention relates to a system for preparing the mating ends of rootstock and scions for grafting and is particularly well suited for softwood grafting operations (sometimes referred to as "green grafting" or "herbaceous grafting").
Grafting typically involves the end-to-end connection of a scion to a rootstock of comparable diameter. Several types of graft unions are known, one of the most common being a tapered cut joint (or "cleft" graft) in which the scion end is trimmed to have a wedge or "V" shaped cross-section, and the stock end is slit longitudinally down its center to provide a mating slot to receive the trimmed scion end. Historically, the scion and stock ends were trimmed by hand, a relatively unsafe and inefficient procedure that produces grafts of inconsistent quality, dependent upon the skill of the manual laborer. In modern times, however, most stock ends are prepared using a mechanical cutter.
Green grafting involves the end-to-end connection of relatively immature, fragile scions to rootstock of comparable diameter. In this application, the step of trimming and joining the stock and scion ends is even more critical and requires greater precision than grafting procedures involving lignified plant material because less plant tissue is available to promote a successful graft. Green grafting typically involves scion and rootstock diameters between 2.5 and 10 mm, whereas dormant bench grafting typically involves diameters of 5 to 15 mm. Thus, there generally is less margin for error in cutting for green grafting. Also, the non-lignified soft plant tissue is more susceptible to drying out and more vulnerable to various diseases. As a result, efforts have been made to develop more effective ways of trimming scion and stock ends, especially those used in green grafting operations. Today, most bench grafts are done with machine cutters.
However, prior attempts to develop machines for trimming scion and stock ends have not been entirely satisfactory. See, for example, U.S. Pat. No. 3,680,255 to Grigorov, U.S. Pat. No. 3,969,843 to Whaler et al., and U.S. Pat. No. 4,769,944 to Fresne et al.
Many, if not all, of the prior machines trim the scion using blades that drop perpendicular to the longitudinal axis of the scion. Thus, the blades cut against the "grain" of the scion, which tends to smash the scion, tearing the tissue, rather than cleanly cutting through the scion. A less clean scion cut decreases the likelihood of a successful graft.
The scions cut by prior art machines are less likely to produce successful grafts than scions cut by hand. It is estimated that hand cutting produces about 15% more successful grafts than prior machines. Thus, to achieve the higher success rate, at least one company still continues to cut their scions for green grafting by hand.
Thus, there remains a need for an improved automatic grafting system which cuts the scion or stock more cleanly, completely, and precisely, without tearing the plant tissue, thereby producing a relatively high percentage of successful grafts. There also remains a need for a system that can be easily operated and maintained, and yet is safer for the operator.